Process for depositing noble metal catalysts

ABSTRACT

A process for depositing a noble metal catalyst on an oxide support material comprising contacting the support material with an alkaline solution of complex noble metal-amine cations under prescribed pH conditions is disclosed. The process is particularly suitable for depositing catalysts on monolithic honeycomb support structures because the catalyst dispersions produced thereby are extremely uniform on the interior channel walls of the structure.

United States Patent Foster et al.

PROCESS FOR DEPOSITING NOBLE METAL CATALYSTS Inventors: Gordon F.Foster, Campbell;

Helmuth E. Meissner, Painted Post; Janice L. Stiles, Corning, all of NY.

Corning Glass Works, Cornin g, N.Y.

Filed: Nov. 9, 1973 Appl. No.: 414,251

Related US. Application Data Continuation-impart of Ser. No. 243,416,April 12, 1972, abandoned.

Assignee:

US. Cl 252/460; 252/466 PT; 252/470; 252/471; 252/472; 252/477 R Int.Cl. B01j 11/08; 8013' 11/06; BOlj ll/22 Field of Search 252/460, 466 PT,472, 451, 252/470, 477 R References Cited UNlTED STATES PATENTS 12/1952Haensal 252/460 X July 15, 1975 3,489,692 l/l970 Bourne et a]. 252/466PT 3,554,929 1/1971 Aarons 252/463 X 3,565,830 2/1971 .Keith et al.252/477 R 3,785,781 l/l974 Hervert et al..... 252/477 R 3,785,998 1/1974Hoekstra 252/477 R Primary Examiner-Carl F. Dees Attorney, Agent, orFzfrml(ees van der Sterre; Clinton S. Janes, Jr.; Clarence R. Patty, Jr.

2 Claims, No Drawings PROCESS FOR DEPOSITING NOBLE METAL CATALYSTS Thisapplication is a continuation-in-part of our copending application Ser.No. 243,416, filed Apr. 12, 1972, now abandoned.

BACKGROUND OF THE INVENTION The present invention has generalapplicability in the field of supported noble metal catalysts systemsand special applicability in the field of supported noble metalcatalysts for the treatment of waste gases, particularly automotiveexhaust gases. It is presently desired to produce small catalytic unitsfor use in automobiles to control harmful exhaust emissions such ascarbon monoxide, unburned hydrocarbons and oxides of nitrogen. To meetgovernment pollution control regulations, such units must attain a veryhigh degree of catalytic efficiency under conditions quite adverse tocatalytic activity and stability.

One promising approach to the automotive emissions control problem hasbeen the use of noble metal catalysts supported on monolithic honeycombsupport structures situated in the exhaust system. These structuresprovide advantages of convenience, compact size and high surfacearea-to-weight ratios which are helpful in maximizing gas-catalystcontact-and, thus, the efficiency of the catalytic unit.

A large number of noble metal catalysts and mixtures have beenconsidered for use in combination with monolithic support structures,and investigation as to the effects of catalyst composition on catalyticstability and efficiency in the exhaust environment has been extensive.In addition, a great deal of attention has been directed to the use ofvarious oxide support materials as coatings on monolithic supportstructures to further promote and stabilize catalytic activity.Nevertheless, it is well known that, together with the nature of thecatalyst and the catalyst support coating, the method of depositing thecatalyst is a most important variable affecting the stability andselectivity of a given catalyst system.

The method of deposition is of particular importance where noble metalcatalysts and monolithic support structures are concerned because of theproblems encountered when it is attempted to employ conventional simpleimpregnation techniques to uniformly distribute noble metal catalysts onthe interior channel walls of a honeycomb structure. Because ofdifferences in liquid evaporation rates between the exterior andinterior surfaces of such structures, dissolved catalyst compounds tendto migrate to the exposed exterior surfaces of the monolith, resultingin highly nonuniform catalyst distribution. This problem is especiallysevere with noble metal catalysts because the solutions employed todeposit noble metals typically contain only minor concentrations ofthese materials. This is because the cost of noble metals makes lowcatalyst loadings highly desirable; however, extremely uniformdispersion is required with low catalyst loadings to produce asufficiently active catalytic unit,

It is the principal object of the present invention to provide asolution to the aforementioned problems in the form of a process foruniformly dispersing minor amounts of noble metal catalysts on oxidecatalyst support materials, particularly on oxide catalyst supportmaterials in the form of monolithic support structures or coatingsthereon.

It is a further object of the present invention to provide a process forthe quantitative deposition of noble metals from noble metal solutionscontaining only minor concentrations of metal in the form of a uniformdispersion on an oxide catalyst support.

Other objects and advantages of the present invention will becomeapparent from the following description and detailed examples thereof.

SUMMARY OF THE INVENTION Our invention includes a process for depositingnoble metal catalysts on certain oxide catalyst support materialscomprising the step of contacting an oxide support material with analkaline aqueous solution of complex noble metal-amine cations under pHconditions such that the complexed noble metal cations will be adsorbedonto the surface of the oxide support. Oxide support materials which maybe treated according to the process of the present invention include atleast partially-hydrated 3- or higher-valent metal oxides such as La OA1 0 Cr O Mn- O TiO 21 02, MnO- SiO SnO ThO and Mn O,,. Partialhydration implies the presence on the oxide support of at least somehydroxyl groups which act as adsorption sites to promote the adsorptionof the desired complex cations.

Because of the requirement for adsorption sites, anhydrous orhydroxyl-free oxide support materials which are to be treated accordingto the process of the present invention should be at least partiallyrehydrated to promote good adsorption. This will occur to some degreeduring contact with the aqueous alkaline catalyst solution, but it maybe accelerated by a pretreatment comprising contacting the oxide withconcentrated aqueous NH containing solutions. Even in the case ofhydrated oxides, this pretreatment may be advantageous because it leadsto the formation of NH, sites on the oxide which promote catalystadsorption through an ammonium-for-complexed catalyst cation exchangereaction.

The pH conditions of the deposition process are controlled by adjustingthe pH of the catalyst solution to a value at least sufficient to permitthe adsorption of the complexed noble metal cations onto the selectedmetal oxide upon contact therewith. Among the noble metal catalystswhich may be suitably deposited according to the invention are platinum,palladium, rhodium, iridium and ruthenium.

Following the adsorption of the catalyst onto the oxide supportmaterial, the further steps of drying, reduction to the metallic stateand firing to remove reaction by-products and bonded water may beaccomplished using procedures known in the art. The resulting supportedcatalyst comprises a useful device for the treatment of waste gases orfor a variety of other catalytic applications.

Although this type of catalyst deposition by adsorption results in ahigh degree of dispersion of noble metal catalyst, an even moreeffective dispersion may be achieved by applying the intended catalystloading to the support structure not in a simple one-step process but inmultiple steps, firing between the steps to decompose the noble metalcompounds to the metal. Superior activity and stability of the noblemetal catalyst can result from such adeposition method.

3 DESCRIPTION OF THE PREFERRED EMBODIMENTS While the process of thepresent invention is generally useful for the deposition of noble metalcatalysts on oxide support materials in any form, it is particularlyuseful in obtaining a uniform dispersion on monolithic honeycombstructures to be employed as catalyst supports. Examples of thesestructures and methods for preparing them are described in the patent toHollenbach, US. Pat. No. 3,112,184. Typically, such honeycombs areformed of refractory ceramic or glassceramic materials composed ofcordierite, spodumene, petalite, silica, alumina, zirconia, magnesia,titania or any other of a wide variety of crystalline or semicrystallinecompounds or solid solutions of refractory metal oxides.

In cases where the selected support structure is composed of silica,alumina, zirconia, titania or any other of the 3- or higher-valent metaloxides which may be treated according to the present invention, noblemetal catalysts may be directly deposited thereon employing thetechniques and procedures herein disclosed. Ordinarily, however, theselected refractory support structure will be composed of a material oflimited suitability as the sole catalyst support, and a suitable oxidesupport material in the form of a coating on the support structure willthen be provided prior to treatment according to the process of thepresent invention.

Whether the oxide support material to be treated according to theinvention is in the form of a coating on a refractory honeycombstructure or in any other form, it is desirable from the standpoint ofcatalyst dispersion that the surface area of the oxide support materialbe high. For example, we have found that surface areas as measured bystandard B.E.T. nitrogen adsorption methods of about to square metersper gram should be provided to obtain relatively low noble metalloadings of about 0.1% by weight on a honeycomb support.

Although the coating of oxide support materials may be provided byanyone of the numerous means known in the art, particularly desirablecoatings may be produced according to the methods described in thecopending application of G. F. Foster and H. E. Meissner, Ser. No.243,417, entitled Support Coatings for Catalysts," commonly assignedherewith. Those methods generally comprise the in situ hydrolysis ofmetal alkoxide-coated monoliths to produce hydrous oxide coatings ofvery high surface area and porosity. Alternatively, we prefer to employmethods described in the copending application of G. F. Foster, H. E.Meissner and J. L. Stiles, Ser. No. 249,353, entitled Process forDepositing Oxide Coatings, commonly assigned herewith. Those methodscomprise the in situ precipitation onto a support structure of certainmetals which form relatively insoluble hydroxides in the presence ofexcess NH OH. The disclosures of each of these two copendingapplications are expressly incorporated herein, and reference may bemade thereto for further explanation of these matters.

While any of the at least partially-hydrated metal oxide supportmaterials described above may be treated according to our process, weparticularly prefer to treat supports composed of amphoteric hydrousoxides, oxihydrates, or hydroxides of 3-and 4-valent metals prepared bythe processes described in the aforementioned applications, particularlyincluding hydrous.

CRgOg, MnO ,Mn O Ml'l- O3, ZI'Og, Slog, SD02,

ThO and A1 0 These may in certain instances be subjected to a heattreatment prior to the catalyst deposition to develop optimum porestructure and stability of the high surface area oxides. Such processesare shown in more detail in the examples of our invention which appearbelow.

Treatment of oxide support materials according to the process of thepresent invention involves contacting the selected support material withan alkaline aqueous solution of complex noble metalamine cations. Noblemetal salts are known to form ammonia complexes with excess ammoniumhydroxide or ammonium carbonate. Thus, solutions of complexed platinum,palladium, rhodium, iridium and ruthenium may be prepared by addingconcentrated or somewhat diluted NH OH to solid or dissolved noble metalchlorides such as H PtCl .6H O, PdCl (NH PtCl RhCl .3H O, lrCl H O, (NHIrCl or RuCl .H O, or in some cases with nitrate compounds of thesemetals. Typically, ammonium hydroxide solutions wherein the weight ratioof concentrated ammonium hydroxide to water ranges from about 1 to 4 toabout 1 to 9 are employed. An initially-formed precipitate with theammonia-alkaline solution disappears during digestion of the resultingsuspension at 100C. for 46 hours. Means such as covered containersshould be provided for controlling the volatilization of ammonia duringthe digestion process. The resulting solutions are stable after coolingto room temperature.

The concentration of amine-complexed noble metal ions in the alkalinesolution is not critical to the effectiveness of the depositionprocedure; adsorption of cations will occur under the prescribedconditions until limited either by the absence of sufficient adsorptionsites on the support under treatment or the depletion of complexedcatalyst cations from the solution. We prefer to limit the volume of thesolution to that just sufficient to completely contact the supportstructures to be treated, and to limit the catalyst concentration tothat amount of catalyst required or attainable with the selectedcatalytic system to be produced.

Quantitative or nearly-quantitative adsorption of the noble metal fromthe solution is particularly desirable from the standpoint both of costand control of catalyst loading, and we have found that quantitativeadsorption of noble metal catalysts in amounts ranging from about0.5-1.0% by weight of the selected honeycomb support structure may beroutinely obtained with certain of our preferred amphoteric hydrousoxide support materials. Such catalyst loadings are more than sufficientto produce an extremely active catalytic unit when dispersed with theuniformity attainable with our process.

Table I below shows several examples of quantitative deposition for somerepresentative catalysts and oxide supports. The alumina and zirconiaoxide supports were deposited on the refractory support structures bythe in situ hydrolysis of aluminum and zirconium alkoxides, while the MnO support was deposited by precipitation with ammonium hydroxide. TableI shows the composition of the support structure and the supportcoating, the catalyst employed, the desired catalyst loading, expressedin percent by weight of the oxidecoated support structure, the amount ofmetal in the alkaline amine solution. and the amount of metal actuallydeposited on the oxide-coated support structure. All of the aminesolutions were prepared by mixing weighed amounts of noble metalcompounds with ammonium hydroxide solutions containing concentratedammonium hydroxide and water in a weight ratio of about 1 to 4. Thetwo-component oxide support coatings shown are layered coatings composedof a base layer of alumina and a covering layer of either zirconiaAlthough there is some evidence that the adsorption of complex noblemetal-amine cations onto the support oxide proceeds quite rapidly uponinitial contact with the alkaline solution, particularly in thepreferred pH or manganese oxide. 5 ranges, a better degree of dispersioncan often be TABLE I Support Catalyst Catalyst Catalyst CatalystStructure Support Composition Loading in Solution on Sample CompositionCoating (weight 7:) (weight (grams) (grams) cordierite Al O -ZrO Pt 0.20.040 0.0397 cordierite A1.o .-Mn,o, Pt 0.2 0.040 0.040 cordierite Al O-M n 0, Pt 0.5 0.100 0.100 aluminonone Pt-307r Rh 0 2 0.794 (Pt) 0.790

silicate 0.340 (Rh) 0.339 cordierite ALO Pt 0.2 0.040 0.0383

The results shown in Table I are readily reproducible achieved byredistribution reactions which occur over with our preferred hydratedalumina, zirconia, silica or longer time periods. For this purpose,contact with the Mn O support materials at loadings below about-0.5%alkaline amine solution may usefully be continued for by weight ofeither platinum, ruthenium, rhodium or periods up to about 24 hours.iridium. Palladium complexes tend to be adsorbed An optional butoften-employed further step in our somewhat less completely, and certainother hydrated 5 deposition process involves the pretreatment of theOxides do not Provide quite as effieleht adsorption, but oxide supportcoating with concentrated aqueous soluuseful catalyst loadings may beobtained with any of the {ions f i m m d Thi procedure fdcatalyst-support systems herein sc o tates catalyst adsorption,particularly in the case of the Our preferred amphoteric hydrated oxidesupp l't less reactive anhydrous oxides, by promoting rehydramaterialsmay act either as cation or anion adsorbers i d th f ti f ()NH, sitefrom O-H depending p the P of the Solution the degree of sites on thesupport material. Upon later contact bebasielty of the metal ions makingi the Oxide and the tween the pretreated oxide support and thealkalinestl'ehgth of the metal-Oxygen bond relative to the aminecatalyst solution, adsorption of the catalyst progeh-hydregeh bond ofthe hydrated Oxide in an q ceeds quite readily through an ammonium-for-OUS ehvhohmeht- The P value of the zero'polht'of' complexed catalystcation exchange reaction. Typi- Charge of the pp with respect to Ht andOH lohs cally, our pretreatment step comprises contacting the in theaqueous environment represents the borderline Oxide support materialwith a concentrated ammonium between acid and base properties. At pHvalues below hwiroxidewater mixture (Concentrated NH4OH to thezero-point-of-charge, anions are preferentially ad- H2O ratio about 1 to1 by weight) by immersion a sorbed. while at pH values above this pointcations are 40 room temperature for 24 hours o course, Sho'rteradserbed- Whlle there is he abrupt change between treatments for periodsof time at least sufficient to sorption of cations and adsorption ofanions to the supcause some adsorption of ions are a|so useful portsurface, it will be appreciated that the adsorption and concentratgds'oluti'bns containing other ammo of cationic noble metal-aminecomplexes will be fanium compounds u NHANO3 or (NHOzCO3 may be veretjland will l' more extensively in hlghlyelkahhe substituted for theconcentrated ammonium hydroxide Selhtlohs' Thus Whlle the PH Valuealkahheeom' solution, if desired. In addition, the effect ofpretreattion should normally be at least sufficient to permit the mentmay be incidentally Obtained through the use of adsothtioh 9 Cationsonto the Selected oxide Support certain of our oxide depositionprocedures involving material, it is preferred that the selected pHvalue be alkoxide hydrolysis or hydroxide precipitation with above theValue assoelhtetl wtth the zetofpolht'of' NH OH, since these proceduresinherently result in the charge of the selected catalyst supportmaterial. Alkapresence of some sites on the Support coating hheSolutions wherein e PH value ranges from about Since our alkaline noblemetal-amine solutions are 3 2 2 1 32225; g g:1 ;gfggggsgg j g g zztcapable dissolving certain amounts of support oxides in the literaturefor many of our oxide support materi 5 Suchas to a lesser extent alu-mmafrom the 5 coating, it IS in many cases desirable to rinse any excessals, but the values for some of our preferred materials CatalystSolution from the oxide Support after the are reproduced below m TableIt: sorption treatment is concluded. In this way, evapora- TABLE IItionof the depleted catalyst solution and precipitation of dissolvedoxide back onto the adsorbed catalyst is H v l A d prevented, andoptimum catalytic activity will be as- Oxidc Support Material with zero-h int t z htirge Sured m t tzompleted unlt' Following rinsing, thesupport with adsorbed catalyst l'z tt 9.1 2 3) may be dried andsubjected to reducing treatments to T102 6 2T0 4 convert the catalyst tothe metallic state by any of the t me, 3 various procedures known in theart. We prefer to 31% i carry out the drying step at moderately elevatedtemperatures, e.g., C., to accelerate the evaporation about 300C. in avacuum for at leastabout an hour to remove the water. of hydration fromthe oxide support material, reduction of the catalyst at 300C. for anhour with flowing forming gas (90% N 10% H; by volume),

and gradual cooling of the support to about 100C. prior to use.Experimental results indicate, however, that the above heating scheduledoes not have a critical relationship to the catalytic activity andstability of the final supported catalyst system, and any treatmentwhich will immobilize the catalyst and dehydrate the coating withoutaffecting the uniformity of the catalyst dispersion may alternatively beemployed.

The following detailed examples more completely illu's tratethepreparation of an active catalytic device using the catalyst depositionprocess of the present inve ntion. These examples are, of course, notlimiting as to the scope of the present invention but are rather merelyillustrative of the kinds of techniques which may be employed incarrying out our process.

EXAMPLE I A monolithic cordierite ceramic structure of cylindrical shapewith about 1 inch diameter and 2-5/16 inch height, comprising about 200cells per square inch of cross sectional area, was coated with 1.18grams of hy- The catalyst-containing solution was prepared bydissolving0;O637 grams of (NHQ PtCl and 0.0307 grams of RhCl .3H O in asolution composed of 1 part concentrated NH OH and 9 parts H O byweight, digesting 1 at 80-90C. for several hours in a covered container.The volume of this solution was adjusted to 30 cc by v the additionofmore of the NH Ol-l solution, with the total platinum content of thesolution being 0.028

grams and the total rhodium content being about 0.012

am After contacting the sample with this catalyst solution for 24 hoursat room temperature, the sample was removed, washed with H 0, and driedat 120C. for 2 ,hours. Virtually all of the noble metal was evenlyadsorbed in the form of amine-complexed cations onto the silica coatingof the support structure. Then the sample was transferred to a furnacewhere it was heated in vacuum to 300C. A gas mixture consisting of 90%nitrogen and 10% hydrogen was introduced at 300C., and a low flow ratethrough the sample was maintained for 1 hour. Then the sample wasallowed to cool. This heat treatment resulted in the decomposition ofthe noble metal compound to reduced noble metal 4 and volatilized,undesirable reaction by-products. The

. device thus produced had a noble metal dispersion composed of about70% platinum and 30% rhodium which comprised about 0.2% by weight of thestructure, evenly distributed over the surface thereof. It was quiteuseful for the catalytic treatment of gases.-

1 EXAMPLE u A cordierite ceramic monolithic substrate of cylindricalshape 1 inch diameter and 2-5/l6 inch height) with about 200 parallelchannels per square inch of cross sectional area was coated withhigh-surface-area alumina by repeated immersion into a melt of aluminumisopropoxide at l00120C. and subsequent hydrolysis in a steam atmosphereat C. (at 18 psi) for 30 minutes. Aftcr heating the sample to 600C. for2 hours, a weight increase of 1.25 grams due to the alumina coating wasobserved.

A coating of manganese oxide (Mn O was applied on top of the alumina byimpregnating the sample with a 50% solution of manganous nitrate,removing excess solution, and precipitating hydrated manganese oxidewith a mixture composed of equal weights of concentrated NH OH andwater. After firing for 4 hours to 500C., a weight gain of 1.81 gramswas observed.

The sample was then treated with a solution composed of equal weights ofconcentrated NH Ol-l and water for 24 hours, and thereafter immersed ina catalyst solution containing 0.040 grams of platinum which wasprepared from 0.0910 grams of (Nl-lg- PtCl and about 30 cc of ammoniumhydroxide solution according to the procedure described in Example 1.After 24 hours of immersionin this solution, the sample was removed,washed, dried and fired according to the procedure of Example 1.Quantitative adsorption of the platinum in solution resulted in acatalytically active dispersion comprising about 0.2% by weight of thehoneycomb structure.

EXAMPLE 111 Two honeycomb cordierite monolithic support structures ofcylindrical shape (3 inch height and 3.6 inch diameter) with about 200parallel channels per square inch of cross sectional area, are coatedwith highsurface-area alumina by immersion into a melt of aluminumisopropoxide at l00l20C. and subsequent hydrolysis in a steam atmosphereat 120C. (18 psi) for 30 minutes. After steam treatment, the samples areheated to 600C. for 2 hours to convert the coating to alumina.

The alumina-coated monoliths prepared as described are provided with aplatinum catalyst. One monolith is platinum-coated by a prior artprocess comprising immersion in an aqueous chloroplatinic acid solutionfor several minutes, removal and shaking to remove excess solution,drying at C. for several minutes to remove water, and firing at 600C.for one hour to convert the chloroplatinic acid to platinum. Theplatinum loading by this process is 0.037 grams of Pt per cubic inch ofmonolithic support.

The second alumina-coated monolithic support is provided with a platinumcoating according to the procedure described above in Example 11,wherein it is immersed in a solution of (NH PtCl in aqueous ammoniumhydroxide (1 part NlhOl-l and 9 parts H O by weight) for 24 hours,removed and washed with H2 dried at 120C. for 2 hours, and fired at300C. in a reducing atmosphere. The platinum loading by this process is0.024 grams of platinum per cubic inch of monolithic support.

Comparison of the catalytic efficiencies of prior art and ion-exchangedhoneycomb devices such as above described indicate that devices preparedaccording to the prior art process do not typically demonstrate theincreased hydrocarbon and carbon monoxide oxidation activity which wouldbe expected in view of the substantially increased (150%) concentrationof platinum thereon. in addition, their resistance to degradation uponexposure to elevated temperatures (e.g. 800C.) is less than would beexpected.

Investigation of the causes of these deficiencies discloses that thereis a substantial maldistribution of platinum throughout the volume ofthe honeycomb device prepared according to the prior art process. Visualinspection shows that, when split parallel to the cylinder axis, thehoneycomb has dark edges but a very lightcolored core, indicatingserious migration of the platinum to the exposed drying surfaces of thedevice. This visual indication is confirmed by wet chemical analysisshowing platinum concentrations as low as .01 1 grams per cubic inch atthe core of the device and concentrations as high as 0.087 grams percubic inch at the periphery.

In contrast to the above findings, examination of the honeycomb deviceprepared according to the invention shows a surprisingly uniformdistribution of platinum on the interior channel walls of the honeycombthroughout the volume of the device. Hence, measurements on this deviceindicate that, in a honeycomb wherein the nominal platinum loading isabout 0024 grams of platinum per cubic inch of honeycomb volume,concentration variations throughout the volume of the device may beroutinely held within the range of about 0.022-0.024 grams of platinumper cubic inch of volume, if desired. The advantages in terms ofefficient usage of expensive noble metal catalysts are readily apparent.

The foregoing examples clearly illustrate the utility of our process toapply minor amounts of noble metal catalysts in the form of extremelyuniform dispersions, particularly in the case of monolithic supportstructures of the honeycomb type which have proven difficult to coatuniformly using prior art processes. Our process, therefore, representsa useful advance in the field of noble metal catalyst depositiontechniques.

We claim:

1. In a process for the deposition of a noble metal catalyst on arefractory monolithic honeycomb support structure which comprises thesteps of providingat least the interior channel walls of the structurewith an oxide support coating, applying a solution of a noble metalcompound to the oxide-coated structure, drying the structure, andtreating the structure with a reducing agent to reduce the noble metalcompound to the metallic state, the improvement which comprises:

a. providing in substitution for said oxide support coating a coatingconsisting of at least one amphoteric hydrous oxide, oxihydrate orhydroxide selected from the group consisting of hydrous Cr O M1102, Mn OM11203, TiO ZtO SiO snog,

Th0 and N 0 on the interior channel walls of said structure;

b. immersing said structure and coating into a catalyst solutionconsisting essentially of water, ammonium hydroxide and at least onenoble metal compound selected from the group consisting of compounds ofplatinum, palladium, rhodium, iridium and ruthenium which form complexnoble metal amine cations in ammonia alkaline solutions, said catalystsolution containing ammonium hydroxide in an amount sufficient to bringthe pH of said catalyst solution within the range of about l0-l LS;

c. removing said structure from said catalyst solution and removingexcess catalyst solution from said structure by rinsing;

d. drying said structure; and

. treating said structure with a reducing agent to reduce the noblemetal compounds thereon to the metallic state.

2. A process for obtaining quantitative adsorption of a noble metalcatalyst from a catalyst solution onto a refractory monolithic honeycombsupport structure which comprises the steps of:

a. providing a coating consisting of at least one amphoteric hydrousoxide, oxihydrate or hydroxide selected from the group consisting ofhydrous Al- O ZrO- SiO and Mn O on at least the interior channel wallsof said structure;

b. immersing said structure and coating into a cata- V lyst solutionconsisting essentially of water, ammonium hydroxide, and at least onenoble metal compound selected from the group consisting of compounds ofplatinum, ruthenium, rhodium and iridium which form complex noble metalamine cations in ammonia alkaline solutions, said noble metal compoundbeing present in said catalyst solution in an amount sufficient toprovide a weight of noble metal constituting about 02-05% of the weightof said structure, and ammonium hydroxide being present in said catalystsolution in an amount sufficient to bring the pH of said catalystsolution within the range of 10-1 1.5, and said solution having a volumejust sufficient to completely contact said structure;

c. removing said structure from said catalyst solution and removingexcess catalyst solution from said structure by rinsing;

d. drying said structure; and

e. treating said structure with a reducing agent to reduce noble metalcompounds thereon to the metallic state.

1. IN A PROCESS FOR THE DEPOSITION OF A NOBLE METAL CATALYST ON AREFRACTORY MONOLITHIC HONEYCOMB SUPPORT STRUCTURE WHICH COMPRISES THESTEPS OF PROVIDING AT LEAST THE INTERIOR CHANNEL WALLS OF THE STRUCTUREWITH AN OXIDE SUPPORT COATING, APPLYING A SOLUTION OF A NOBLE METALCOMPOUND TO THE OXIDECOATED STRUCTURE, DRYING THE STRUCTURE, ANDTREATING THE STRUCTURE WITH A REDUCING AGENT TO REDUCE THE NOBLE METALCOMPOUND TO THE METALLIC STATE, THE IMPROVEMENT WHICH COMPRISES: A.PROVIDING IN SUBSTITUTION FOR SAID OXIDE SUPPORT COATING A COATINGCONSISTING OF AT LEAST ONE AMPHOTERIC HYDROUS OXIDE, OXIHYDRATE ORHYDROXIDE SELECTED FROM THE GROUP CONSISTING OF HYDROUS CR2O3, MNO2,MN3O4, MN2O3, TIO2, ZRO2, SIO2, SNO2, THO2 AND AL2O3 ON THE INTERIORCHANNEL WALLS OF SAID STRUCTURE, B. IMMERSING SAID STRUCTURE AND COATINGINTO A CATALYST SOLUTION CONSISTING ESSENTIALLY OF WATER, AMMONIUMHYDROXIDE AND AT LEAST ONE NOBLE METAL COMPOUND SELECTED FROM THE GROUPCONSISTING OF COMPOUNDS OF PLATINUM, PALLADIUM, RHODIUM, IRIDIUM ANDRUTHENIUM WHICH FORM COMPLEX NOBLE METAL AMINE CATIONS IN AMMONIAALKALINE SOLUTIONS, SAID CATALYST SOLUTION CONTAINING AMMONIUM HYDROXIDEIN AN AMOUNT SUFFICIENT TO BRING THE PH OF SAID CATALYST SOLUTION WITHINTHE RANGE OF ABOUT 10-11.5, C. REMOVING SAID STRUCTURE FROM SAIDCATALYST SOLUTION AND REMOVING EXCESS CATALYST SOLUTION FROM SAIDSTRUCTURE BY RISING, D. DRYING SAID STRUCTURE, AND E. TREATING SAIDSTRUCTURE WITH A REDUCING AGENT TO REDUCE THE NOBLE METAL COMPOUNDSTHEREON TO THE METALLIC STATE.
 2. A process for obtaining quantitativeadsorption of a noble metal catalyst from a catalyst solution onto arefractory monolithic honeycomb support structure which comprises thesteps of: a. providing a coating consisting of at least one amphoterichydrous oxide, oxihydrate or hydroxide selected from the groupconsisting of hydrous Al2O3, ZrO2, SiO2 and Mn3O4 on at least theinterior channel walls of said structure; b. immersing said structureand coating into a catalyst solution consisting essentially of water,ammonium hydroxide, and at least one noble metal compound selected fromthe group consisting of compounds of platinum, ruthenium, rhodium andiridium which form complex noble metal amine cations in ammonia alkalinesolutions, said noble metal compound being present in said catalystsolution in an amount sufficient to provide a weight of noble metalconstituting about 0.2-0.5% of the weight of said structure, andammonium hydroxide being present in said catalyst solution in an amountsufficient to bring the pH of said catalyst solution within the range of10-11.5, and said solution having a volume just sufficient to completelycontact said structure; c. removing said structure from said catalystsolution and removing excess catalyst solution from said structure byrinsing; d. drying said structure; and e. treating said structure with areducing agent to reduce noble metal compounds thereon to the metallicstate.